JP2012248569A - Polishing agent and polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To polish a non-oxide single crystal substrate, such as a silicon carbide single crystal substrate, with high polishing speed, thereby obtaining a high quality surface smooth and excellent in surface characteristics even at an atomic level of a crystal.SOLUTION: A polishing agent for chemically mechanically polishing a non-oxide single crystal substrate contains: an oxidant including transition metal having an oxidation reduction potential of 0.5 V or greater; a cerium oxide particle having an average secondary particle size of 0.5 μm or less; and a dispersion medium. In the polishing agent of the present invention, the oxidant is preferably a permanganate ion. The polishing agent has preferably a pH of 11 or less.

Description

  The present invention relates to an abrasive and a polishing method for chemically and mechanically polishing a non-oxide single crystal substrate. More specifically, the present invention relates to an abrasive suitable for finish polishing of a silicon carbide single crystal substrate or the like, and a polishing method using the same.

  Silicon carbide (SiC) semiconductors have a higher breakdown electric field, electron saturation drift velocity, and thermal conductivity than silicon semiconductors, so silicon carbide semiconductors can be operated at higher temperatures and higher speeds than conventional silicon devices. Research and development to realize power devices has been conducted. In particular, the development of a highly efficient switching element used as a power source for driving a motor of an electric motorcycle, an electric vehicle, a hybrid car or the like has attracted attention. In order to realize such a power device, a silicon carbide single crystal substrate having a smooth surface for epitaxial growth of a high-quality silicon carbide semiconductor layer is required.

  Also, blue laser diodes are attracting attention as light sources for recording information at high density, and there is an increasing need for white diodes as light sources that replace fluorescent lamps and light bulbs. Such a light-emitting element is manufactured using a gallium nitride (GaN) semiconductor, and a silicon carbide single crystal substrate is used as a substrate for forming a high-quality gallium nitride semiconductor layer.

  A silicon carbide single crystal substrate for such applications requires high processing accuracy in terms of the flatness of the substrate, the smoothness of the substrate surface, and the like. However, since the silicon carbide single crystal has extremely high hardness and excellent corrosion resistance, the workability in producing a substrate is poor, and it is difficult to obtain a silicon carbide single crystal substrate having high smoothness.

  In general, a smooth surface of a semiconductor single crystal substrate is formed by polishing. When polishing a silicon carbide single crystal, the surface is mechanically polished using abrasive grains such as diamond harder than silicon carbide as an abrasive to form a flat surface, but a silicon carbide single crystal substrate polished with diamond abrasive grains A minute scratch corresponding to the grain size of the diamond abrasive grains is introduced on the surface of the. In addition, since a work-affected layer having mechanical strain is generated on the surface, the smoothness of the surface of the silicon carbide single crystal substrate is not sufficient as it is.

  In the manufacture of a semiconductor single crystal substrate, a chemical mechanical polishing (hereinafter sometimes referred to as CMP) technique is used as a method of smoothing the surface of a semiconductor substrate after mechanical polishing. CMP uses a chemical reaction such as oxidation to convert a workpiece into an oxide or the like, and polishes the surface by removing the generated oxide using abrasive grains having a hardness lower than that of the workpiece. Is the method. This method has the advantage that an extremely smooth surface can be formed without causing distortion on the surface of the workpiece.

  Conventionally, a polishing composition having a pH of 4 to 9 containing colloidal silica is known as an abrasive for smoothly polishing the surface of a silicon carbide single crystal substrate by CMP (see, for example, Patent Document 1). A polishing composition containing silica abrasive grains, an oxidizing agent (oxygen donor) such as hydrogen peroxide, and a vanadate has also been proposed (see, for example, Patent Document 2).

However, there has been a problem that the polishing rate of the silicon carbide single crystal substrate by the polishing composition of Patent Document 1 is low and the time required for polishing becomes very long.
In addition, when the polishing composition of Patent Document 2 is used, there is a problem that the polishing rate is not sufficient and the polishing takes time. Furthermore, when the polishing composition of Patent Document 2 is used, when the surface properties of the polished silicon carbide single crystal substrate are observed with a microscope, damage such as irregularities and burrows is observed at the front part of the atomic step of the crystal. There was a problem of being. Furthermore, a method of smoothly polishing the surface of a silicon carbide single crystal substrate or the like using silicon oxide (silica) and cerium oxide (ceria) abrasive grains in the presence of an oxidizing polishing liquid has been proposed (for example, Non-patent document 1). However, the method described in Non-Patent Document 1 has a problem that damage such as scratches and distortions is caused on the surface due to the strong mechanical action of the abrasive grains having a very large particle diameter.

Japanese Patent Laid-Open No. 2005-117027 JP 2008-179655 A

Abrasives Processing Journal Vol.53 No.7 2009 Jul 417-420

  The present invention has been made to solve such problems. A non-oxide single crystal substrate having a high hardness and high chemical stability, such as a silicon carbide single crystal substrate, is polished at a high polishing rate and smoothed. An object of the present invention is to provide a polishing agent and a polishing method for obtaining a high-quality surface excellent in surface properties even at the atomic level of crystals.

  The polishing agent of the present invention is a polishing agent for chemically and mechanically polishing a non-oxide single crystal substrate, and includes an oxidizing agent containing a transition metal having a redox potential of 0.5 V or more, and average secondary particles. It contains cerium oxide particles having a diameter of 0.5 μm or less and a dispersion medium.

  In the polishing agent of the present invention, the oxidizing agent is preferably a permanganate ion. And it is preferable that content of the said permanganate ion is 0.015 mass% or more and 5 mass% or less. Moreover, it is preferable that the average secondary particle diameter of the said cerium oxide particle is 0.2 micrometer or less. And it is preferable that content of the said cerium oxide particle is 0.01 mass% or more and 10 mass% or less.

  Furthermore, the abrasive of the present invention has a pH of preferably 11 or less, and more preferably 5 or less. Furthermore, the non-oxide single crystal substrate can be a silicon carbide single crystal substrate or a gallium nitride single crystal substrate.

  In the polishing method of the present invention, a polishing agent is supplied to a polishing pad, the surface to be polished of a non-oxide single crystal substrate that is an object to be polished is brought into contact with the polishing pad, and polishing is performed by relative movement between the two. In the method, the abrasive according to the present invention is used as the abrasive.

According to the polishing agent of the present invention and the polishing method using the same, the surface to be polished of a non-oxide single crystal substrate having high hardness and high chemical stability such as a silicon carbide single crystal substrate or a gallium nitride single crystal substrate can be obtained. The surface to be polished can be polished at a high polishing rate, and the surface to be polished is flat and smooth and excellent in surface properties even at the atomic level.
In the present invention, the “surface to be polished” is a surface to be polished of an object to be polished, such as a surface.

It is a figure which shows an example of the grinding | polishing apparatus which can be used for embodiment of the grinding | polishing method of this invention. It is a top view which shows typically the surface property of the crystal atom level in the board | substrate after grinding | polishing.

  Embodiments of the present invention will be described below.

[Abrasive]
The abrasive of the present invention is an abrasive for chemically and mechanically polishing a non-oxide single crystal substrate, and is an oxidizer containing a transition metal having a redox potential of 0.5 V or more, and abrasive grains. It contains cerium oxide particles having an average secondary particle size of 0.5 μm or less and a dispersion medium, and has a slurry shape.

  The abrasive of the present invention contains an oxidant containing a transition metal having a redox potential of 0.5 V or more and cerium oxide particles having an average secondary particle diameter of 0.5 μm or less. Such a polished surface of an object to be polished having high hardness and high chemical stability can be polished at a high polishing rate, and a surface that is flat and smooth and excellent in surface properties at the atomic level of crystals can be obtained.

  In addition, it is preferable that pH of the abrasive | polishing agent of this invention shall be 11 or less. In order to adjust the pH to 11 or less, a pH adjuster can be added. When the pH of the abrasive is 11 or less, the oxidizing agent acts effectively so that the polishing characteristics are good and the dispersion stability of the cerium oxide particles as the abrasive grains is also excellent. Hereinafter, each component and pH of the abrasive | polishing agent of this invention are explained in full detail.

(Oxidant)
The oxidizing agent contained in the polishing agent of the present invention is to form an oxide layer on the surface to be polished of an object to be described later (for example, a SiC single crystal substrate or a GaN single crystal substrate). By removing this oxide layer from the surface to be polished by mechanical force, polishing of the object to be polished is promoted. That is, compound semiconductors such as SiC and GaN are non-oxides and are difficult to polish, but an oxide layer can be formed on the surface by an oxidizing agent in the polishing agent. Since the formed oxide layer has a lower hardness than the object to be polished and is easily polished, it can be effectively removed by cerium oxide particles that are abrasive grains. As a result, a high polishing rate appears.

  The oxidizing agent contained in the abrasive of the present invention contains a transition metal having a redox potential of 0.5 V or more. Examples of the oxidizing agent containing a transition metal having a redox potential of 0.5 V or more include permanganate ion, vanadate ion, dichromate ion, cerium ammonium nitrate, iron (III) nitrate nonahydrate, silver nitrate, Examples thereof include phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, phosphotungstomolybdic acid, and phosphovanadomolybdic acid. Permanganate ions are particularly preferred. As a source of permanganate ions, permanganate such as potassium permanganate and sodium permanganate is preferable.

The reason why permanganate ions are particularly preferable as an oxidizing agent in polishing a SiC single crystal substrate is shown below.
(1) Permanganate ions have strong oxidizing power to oxidize SiC single crystals.
If the oxidizing power of the oxidizing agent is too weak, the reaction with the polished surface of the SiC single crystal substrate becomes insufficient, and as a result, a sufficiently smooth surface cannot be obtained. An oxidation-reduction potential is used as an index of the oxidizing power with which an oxidizing agent oxidizes a substance. The redox potential of permanganate ions is 1.70 V, and potassium perchlorate (KClO ₄ ) (redox potential 1.20 V) or sodium hypochlorite (NaClO) (redox potential) generally used as an oxidizing agent. Compared with 1.63 V), the redox potential is high.
(2) Permanganate ion has a high reaction rate.
Since permanganate ions have a higher oxidation reaction rate than hydrogen peroxide (oxidation-reduction potential: 1.76 V), which is known as an oxidizing agent with a strong oxidizing power, the oxidizing power is exerted quickly. can do.
(3) Permanganate ions have a low environmental impact.
(4) The permanganate is completely dissolved in the dispersion medium (water) described later. Therefore, the dissolution residue does not adversely affect the smoothness of the substrate.

  In order to obtain the effect of improving the polishing rate, the content (concentration) of permanganate ions in the abrasive is preferably 0.015% by mass or more and 5% by mass or less. If it is less than 0.015% by mass, the effect as an oxidizing agent cannot be expected, and it may take a very long time to form a smooth surface by polishing, or scratches may occur on the surface to be polished. When the content of permanganate ions exceeds 5% by mass, depending on the temperature of the polishing liquid, the permanganate may not be completely dissolved and precipitates, and the solid permanganate comes into contact with the surface to be polished. May cause scratches. The content of permanganate ions contained in the abrasive is more preferably 0.02% by mass to 4% by mass, and particularly preferably 0.05% by mass to 3% by mass.

(Abrasive grains)
The cerium oxide (ceria) particles having an average secondary particle diameter of 0.5 μm or less, which are abrasive grains contained in the abrasive of the present invention, remove an oxide layer formed on the surface to be polished by the oxidant. . Polishing is promoted by polishing this oxide layer by chemical and mechanical action. Further, by using particles having an average secondary particle diameter of 0.5 μm or less, scratches due to mechanical damage to the surface to be polished can be reduced. The average secondary particle diameter of the cerium oxide particles is more preferably 0.2 μm or less.

  In the polishing of the SiC single crystal substrate, when the cerium oxide particles are used together with the above-described oxidizing agent, the polishing rate is increased due to chemical and mechanical action and the surface roughness is higher than when the silica abrasive grains are used. A smooth and smooth surface can be obtained. The reason why cerium oxide particles are particularly preferred is not clear, but cerium oxide particles exhibit a high polishing rate through a chemical reaction with respect to silicon oxide films formed by glass or CVD (Chemical Vapor Deposition). It has been known. In the SiC single crystal substrate, an oxide layer composed of silicon and oxygen is expected to be formed on the surface to be polished by the oxidizing agent, so that the cerium oxide particles and the silicon oxide film by the glass or CVD film forming method are used. It is conceivable that a chemical reaction occurs with the formed oxide layer, and this reaction has an advantage that a polishing promoting effect is expected.

  Further, when cerium oxide particles exceeding the range of the average secondary particle diameter are used as the abrasive grains, damage to the polished surface of the SiC single crystal substrate is large, and a smooth and high-quality surface cannot be obtained. . That is, when polishing is performed using an abrasive containing cerium oxide particles having an average secondary particle diameter of more than 0.5 μm, the step line of crystal atoms of the polished SiC single crystal substrate may be excessively curved or distorted. Damage due to mechanical action. Therefore, there is a possibility that crystal defects or the like may occur in a film such as a silicon carbide semiconductor formed by epitaxial growth on the polished surface.

  In addition, since the cerium oxide particles contained as abrasive grains are usually present as aggregated particles (secondary particles) in which primary particles are aggregated in an abrasive, the average particle diameter of cerium oxide particles is preferably 2 It shall represent with the next particle diameter (average aggregate particle diameter). The average secondary particle diameter is obtained by measuring the cerium oxide particles in the abrasive using, for example, a particle size distribution meter using dynamic light scattering.

  The content ratio (concentration) of the cerium oxide particles in the abrasive of the present invention is preferably 0.01% by mass or more and 10.0% by mass or less in order to obtain a sufficient polishing rate. When the content ratio of the cerium oxide particles is less than 0.01% by mass, it is difficult to obtain a sufficient polishing rate, and when it exceeds 10.0% by mass, the dispersibility is lowered and scratches may occur on the polished surface. . Moreover, there is a problem that the slurry cost increases. A more preferable content rate is 0.02-5.0 mass%, and a more preferable content rate is 0.03-2.0 mass%.

(PH and pH adjuster)
The pH of the abrasive according to the present invention is preferably 11 or less, more preferably 5 or less, and particularly preferably 3 or less, from the viewpoint of polishing characteristics and dispersion stability of cerium oxide particles as abrasive grains. When the pH is 11 or more, the smoothness of the surface to be polished may be deteriorated due to a decrease in dispersibility of the cerium oxide particles.

  The pH of the abrasive of the present invention can be adjusted by adding or blending an acid or basic compound that is a pH adjuster. Examples of acids include inorganic acids such as nitric acid, sulfuric acid, phosphoric acid and hydrochloric acid, saturated carboxylic acids such as formic acid, acetic acid, propionic acid and butyric acid, hydroxy acids such as lactic acid, malic acid and citric acid, phthalic acid and salicylic acid. Organic acids such as aromatic carboxylic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid and other dicarboxylic acids, amino acids, and heterocyclic carboxylic acids can be used. The use of nitric acid and phosphoric acid is preferred, and the use of nitric acid is particularly preferred. As the basic compound, quaternary ammonium compounds such as ammonia, lithium hydroxide, potassium hydroxide, sodium hydroxide and tetramethylammonium, and organic amines such as monoethanolamine, ethylethanolamine, diethanolamine and propylenediamine can be used. Use of potassium hydroxide and sodium hydroxide is preferable, and potassium hydroxide is particularly preferable.

  The content ratio (concentration) of these acids or basic compounds is an amount that adjusts the pH of the abrasive to a predetermined range (pH 11 or less, more preferably 5 or less).

(Dispersion medium)
In the abrasive | polishing agent of this invention, water contains as a dispersion medium. Water is a medium for stably dispersing cerium oxide particles and dispersing / dissolving an oxidizing agent and optional components to be added as necessary. Although there is no restriction | limiting in particular about water, From a viewpoint of the influence with respect to a mixing | blending component, mixing of an impurity, pH, etc., pure water, ultrapure water, and ion-exchange water (deionized water) are preferable.

(Preparation of abrasive and optional components)
The abrasive of the present invention is prepared and used so that the above-described components are contained in the predetermined ratio, the cerium oxide particles are uniformly dispersed, and the other components are uniformly dissolved. . For mixing, a stirring and mixing method usually used in the production of abrasives, for example, a stirring and mixing method using an ultrasonic disperser, a homogenizer or the like can be employed. The abrasive according to the present invention does not necessarily have to be supplied to the polishing site as a mixture of all of the pre-configured polishing components. When supplying to the place of grinding | polishing, a grinding | polishing component may be mixed and it may become a composition of an abrasive | polishing agent.

  The abrasive of the present invention may contain an anti-aggregation agent or dispersant, a lubricant, a chelating agent, a reducing agent, a viscosity-imparting agent or a viscosity modifier, a rust inhibitor, etc. Can be appropriately contained. However, when these additives have the function of an oxidizing agent, an acid, or a basic compound, they are handled as an oxidizing agent, an acid, or a basic compound.

  The dispersant is added to stably disperse cerium oxide particles as abrasive grains in a dispersion medium such as pure water. In addition, the lubricant appropriately adjusts the polishing stress generated between the object to be polished and enables stable polishing. As the dispersant and lubricant, anionic, cationic, nonionic, amphoteric surfactants, polysaccharides, water-soluble polymers and the like can be used. As the surfactant, there are an aliphatic hydrocarbon group and an aromatic hydrocarbon group as a hydrophobic group, and a linking group such as an ester, ether, amide, etc., an acyl group, an alkoxyl group, etc. is included in the hydrophobic group. One having one or more introduced groups and one having a carboxylic acid, a sulfonic acid, a sulfate ester, a phosphoric acid, a phosphate ester or an amino acid can be used as the hydrophilic group. Examples of polysaccharides that can be used include alginic acid, pectin, carboxymethylcellulose, curdlan, pullulan, xanthan gum, carrageenan, gellan gum, locust bean gum, gum arabic, tamarind, and psyllium. As the water-soluble polymer, polyacrylic acid, polyvinyl alcohol, polyvinyl pyrrolidone, polymethacrylic acid, polyacrylamide, polyaspartic acid, polyglutamic acid, polyethyleneimine, polyallylamine, polystyrene sulfonic acid and the like can be used. When using a dispersant and a lubricant, the content is preferably in the range of 0.001 to 5 mass% with respect to the total mass of the abrasive.

[Polishing object]
The polishing object to be polished by the polishing agent of the present invention is a non-oxide single crystal substrate. Examples of non-oxide single crystal substrates include compound semiconductor substrates such as SiC single crystal substrates and GaN single crystal substrates. In particular, by using the abrasive of the present invention for polishing a single crystal substrate having a modified Mohs hardness of 10 or more, such as the SiC single crystal substrate or the GaN single crystal substrate, the effect of high-speed polishing can be further obtained. .

[Polishing method]
As a method of polishing a non-oxide single crystal substrate which is a polishing object using the polishing agent of the present invention, the surface to be polished of the polishing object and the polishing pad are brought into contact while supplying the polishing agent to the polishing pad. A polishing method in which polishing is performed by relative movement between the two is preferable.

In the above polishing method, a conventionally known polishing apparatus can be used as the polishing apparatus.
FIG. 1 shows an example of a polishing apparatus that can be used in the embodiment of the present invention, but the polishing apparatus used in the embodiment of the present invention is not limited to such a structure.

  In the polishing apparatus 10 shown in FIG. 1, a polishing surface plate 1 is provided in a state of being rotatably supported around a vertical axis C 1, and this polishing surface plate 1 is supported by a surface plate driving motor 2. , And is driven to rotate in the direction indicated by the arrow in the figure. A known polishing pad 3 is attached to the upper surface of the polishing surface plate 1.

  On the other hand, a substrate holding member (carrier) 5 for holding a polishing object 4 such as a SiC single crystal substrate on the lower surface by suction or using a holding frame is provided at a position eccentric from the axis C1 on the polishing surface plate 1. It is supported so as to be rotatable about the axis C2 and movable in the direction of the axis C2. The substrate holding member 5 is configured to be rotated in a direction indicated by an arrow by a work drive motor (not shown) or by a rotational moment received from the polishing surface plate 1. A polishing object 4 is held on the lower surface of the substrate holding member 5, that is, the surface facing the polishing pad 3. The polishing object 4 is pressed against the polishing pad 3 with a predetermined load.

  A dripping nozzle 6 is provided in the vicinity of the substrate holding member 5 so that the abrasive 7 of the present invention fed from a tank (not shown) is supplied onto the polishing surface plate 1.

  When polishing by such a polishing apparatus 10, the polishing platen 1 and the polishing pad 3 attached thereto, the substrate holding member 5 and the polishing object 4 held on the lower surface of the polishing platen 1, The polishing object 4 held on the substrate holding member 5 is supplied to the surface of the polishing pad 3 while the polishing agent 7 is supplied to the surface of the polishing pad 3 from the dropping nozzle 6 or the like while being rotated around each axis by the work drive motor. It is pressed against the polishing pad 3. Thereby, the surface to be polished of the polishing object 4, that is, the surface facing the polishing pad 3 is chemically and mechanically polished.

  The substrate holding member 5 may perform a linear motion as well as a rotational motion. Further, the polishing surface plate 1 and the polishing pad 3 do not have to rotate, and may move in one direction, for example, by a belt type.

  The polishing conditions by the polishing apparatus 10 are not particularly limited, but it is possible to increase the polishing pressure and improve the polishing rate by applying a load to the substrate holding member 5 and pressing it against the polishing pad 3. The polishing pressure is preferably about 5 to 80 kPa, and more preferably about 10 to 50 kPa from the viewpoint of polishing rate uniformity in the polished surface, flatness, and prevention of polishing defects such as scratches. The rotation speed of the polishing surface plate 1 and the substrate holding member 5 is preferably about 50 to 500 rpm, but is not limited thereto. The supply amount of the abrasive 7 is appropriately adjusted and selected depending on the constituent material of the surface to be polished, the composition of the polishing liquid, the above polishing conditions, and the like.

  As the polishing pad 3, one made of a general nonwoven fabric, foamed polyurethane, porous resin, non-porous resin or the like can be used. Further, in order to promote the supply of the polishing liquid 7 to the polishing pad 3 or to collect a certain amount of the polishing liquid 7 on the polishing pad 3, the surface of the polishing pad 3 has a lattice shape, a concentric circle shape, a spiral shape, or the like. Groove processing may be performed. Further, if necessary, polishing may be performed while bringing the pad conditioner into contact with the surface of the polishing pad 3 and conditioning the surface of the polishing pad 3.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these Examples. Examples 1 to 16 are examples of the present invention, and Examples 17 to 23 are comparative examples.

(1) Preparation of abrasive (1-1)
Each abrasive | polishing agent of Examples 1-16 was prepared as shown below. First, pure water was added to potassium permanganate, which is an oxidizing agent shown in Table 1, and the mixture was stirred for 10 minutes using a stirring blade. Next, cerium oxide particles having an average secondary particle size of 0.18 μm as abrasive grains were added to this liquid, and after stirring for 10 minutes using a stirring blade, phosphoric acid, nitric acid, potassium hydroxide, Sodium hydroxide was gradually added while stirring to adjust the predetermined pH shown in Table 1 to obtain an abrasive. Table 1 shows the content (concentration: mass%) of each component used in each example with respect to the entire abrasive. In addition, the oxidizing agent density | concentration in Table 1 is not the density | concentration of the permanganate ion which is ion, but the density | concentration of potassium permanganate.

(1-2)
Each abrasive of Examples 17-23 was prepared as shown below. In Example 17, pure water was added to a colloidal silica dispersion having a primary particle diameter of 0.04 μm and an average secondary particle diameter of about 0.07 μm and a silica solid content of about 40% by mass, and a stirring blade was used. Stir for 10 minutes. Next, ammonium vanadate as a metal salt is added to this solution while stirring. Finally, hydrogen peroxide solution is added and stirred for 30 minutes to obtain a polishing agent adjusted to the prescribed component concentrations shown in Table 1. It was. In Examples 18 and 19, cerium oxide particles having an average secondary particle size of 0.18 μm were added to pure water and stirred for 10 minutes using a stirring blade. Subsequently, phosphoric acid and nitric acid were gradually added as a pH adjuster to adjust to a predetermined pH shown in Table 1 to obtain an abrasive. In Example 20, an abrasive was obtained by adjusting in the same manner as in Example 3 except that cerium oxide particles having an average secondary particle size of 1.3 μm were used. In Examples 21 to 23, pure water was added to each of oxidizing agents ammonium persulfate, potassium persulfate, and hydrogen peroxide, and the mixture was stirred for 10 minutes using a stirring blade. Next, cerium oxide particles having an average secondary particle size of 0.18 μm were added to this liquid, and the mixture was stirred for 10 minutes using a stirring blade. As a pH adjuster, potassium hydroxide was added as necessary, and adjusted to a predetermined pH shown in Table 1 to obtain an abrasive. Table 1 shows the content ratio (concentration: mass%) of each component used in each comparative example with respect to the entire abrasive. In addition, the oxidizing agent density | concentration in Table 1 is not the density | concentration of the permanganate ion which is ion, but the density | concentration of potassium permanganate.

  In addition, about the primary particle diameter of the silica particle mix | blended in Example 17, it calculates | requires in conversion from the specific surface area obtained by BET method, and average secondary particle diameter is measured by Microtrac UPA (made by Nikkiso Co., Ltd.). did. About each abrasive | polishing agent other than that, only the average secondary particle diameter was measured by LA920 (made by Horiba Seisakusho).

(1-2) Measurement of pH The pH of each abrasive obtained in Examples 1 to 23 was measured at 25 ° C. using pH81-11 manufactured by Yokogawa Electric Corporation. The measurement results are shown in Table 1.

(2) Evaluation of abrasive properties of abrasives Each abrasive obtained in Examples 1 to 23 was evaluated for abrasive properties by the following method.
(2-1) Polishing conditions As a polishing machine, a polishing apparatus manufactured by MAT was used. As a polishing pad, SUBA800-XY-groove (manufactured by Nitta Haas) was used, and conditioning was performed using a diamond disk before polishing. Further, the polishing was performed for 30 minutes with the supply rate of the abrasive being 25 ml / min, the rotation speed of the polishing platen being 68 rpm, the rotation speed of the substrate holding member being 68 rpm, and the polishing pressure being 5 psi (34.5 kPa).

(2-2) To-be-polished object As a to-be-polished object, a 3 inch diameter 4H-SiC substrate that was pre-polished using diamond abrasive grains was used, and the principal surface (0001) was 0 ° with respect to the C axis. Use a SiC single crystal substrate (On-axis substrate) within + 0.25 ° and an SiC single crystal substrate with an off angle of 4 ° ± 0.5 ° with respect to the C axis of the main surface, respectively, and polish the Si surface side And evaluated.

(2-3) Measurement of polishing rate The polishing rate was evaluated by the amount of change in thickness (nm / hr) per unit time of the SiC single crystal substrate. Specifically, the mass of an unpolished substrate with a known thickness and the mass of the substrate after polishing for each time were measured, and the mass change was determined from the difference. And the change per time of the thickness of the board | substrate calculated | required from this mass change was computed using the following formula. Table 1 shows the calculation results of the polishing rate.
(Calculation formula of polishing rate (V))
Δm = m0−m1
V = Δm / m0 × T0 × 60 / t
(Where, Δm (g) is the mass change before and after polishing, m0 (g) is the initial mass of the unpolished substrate, m1 (g) is the mass of the substrate after polishing, V is the polishing rate (nm / hr), and T0 is (The thickness (nm) of the unpolished substrate and t represents the polishing time (min).)

(2-4) Measurement of atomic step terrace width distribution In the On-axis substrate polished with the abrasives of Example 3 and Example 20, the range of the polished surface having a width of 2 μm and a height of 1 μm was measured by AFM. As shown in FIG. 2, the terrace width of each atomic step was measured at 0.2 μm intervals, and the difference between the maximum value and the minimum value of the terrace width and the standard deviation were obtained.

(2-5) Measurement of average roughness of atomic step front part In the On-axis substrate polished with the abrasives of Example 3 and Example 17, the range of the polished surface width of 2 μm and height of 1 μm was measured by AFM. did. As shown in FIG. 2, the roughness (Ra) was measured for the cross-sectional shape of the front part of each atomic step, and the average value was obtained.

  As can be seen from Table 1, when the abrasives of Examples 1 to 16 were used, a high polishing rate was obtained for both the On-axis substrate and the SiC single crystal substrate having an off angle of 4 ° or less. High-speed polishing is possible. In addition, the atomic step line obtained from the AFM measurement shows no curvature and maintains linearity, the terrace width of each atomic step is uniform, the shape of the front part of the atomic step is not flared, the average Ra was also small and good.

  On the other hand, when the abrasive | polishing agent of Example 17 containing colloidal silica, hydrogen peroxide, and ammonium vanadate is used, a grinding | polishing rate is compared with the case where the abrasive | polishing agent of Examples 1-16 which are an Example is used. It is low. Further, the atomic step front portion obtained by the AFM measurement was confirmed to have a gap, the average Ra was larger than that of Example 3 as an example, and the surface property at the atomic level was poor. When the abrasives of Examples 18 and 19 containing no oxidizing agent were used, the polishing rate was remarkably reduced as compared with the Examples.

  In addition, when the abrasive of Example 20 containing potassium permanganate as an oxidizer and containing cerium oxide particles having an average secondary particle size of 1.3 μm as an abrasive is used, a high polishing rate is exhibited. From the AFM measurement, it was found that due to the curvature of the atomic step due to excessive mechanical action, the variation in the width of each atomic step terrace was large, and the surface properties at the atomic level were poor. Furthermore, when the abrasive | polishing agent of Examples 21-23 which used oxidizing agents other than potassium permanganate as an oxidizing agent was used, the grinding | polishing rate fell remarkably compared with the Example.

  According to the present invention, non-oxide single crystal substrates, particularly SiC single crystal substrates and GaN single crystal substrates, which are high in hardness and high in chemical stability, can be polished at high speed, and are flat with no scratches. In addition, it is possible to obtain a polished surface excellent in smoothness. Therefore, it can contribute to the improvement of productivity of those substrates.

  DESCRIPTION OF SYMBOLS 1 ... Polishing surface plate, 2 ... Surface plate drive motor, 3 ... Polishing pad, 4 ... Polishing target object, 5 ... Substrate holding member, 6 ... Dropping nozzle, 7 ... Polishing agent, 10 ... Polishing apparatus.

Claims (9)

An abrasive for chemically and mechanically polishing a non-oxide single crystal substrate,
A polishing agent comprising an oxidizing agent containing a transition metal having a redox potential of 0.5 V or more, cerium oxide particles having an average secondary particle diameter of 0.5 μm or less, and a dispersion medium.   The abrasive according to claim 1, wherein the oxidizing agent is a permanganate ion.   The abrasive according to claim 2, wherein the content of the permanganate ion is 0.015 mass% or more and 5 mass% or less.   4. The abrasive according to claim 1, wherein an average secondary particle diameter of the cerium oxide particles is 0.2 μm or less.   The abrasive according to any one of claims 1 to 4, wherein the content of the cerium oxide particles is 0.01 mass% or more and 10 mass% or less.   The abrasive according to any one of claims 1 to 5, which has a pH of 11 or less.   The abrasive according to claim 6, having a pH of 5 or less.   The abrasive according to any one of claims 1 to 7, wherein the non-oxide single crystal substrate is a silicon carbide (SiC) single crystal substrate or a gallium nitride (GaN) single crystal substrate.   A method of supplying a polishing agent to a polishing pad, bringing a polishing target surface of a non-oxide single crystal substrate, which is an object to be polished, into contact with the polishing pad, and polishing by relative motion between the two, A polishing method using the abrasive according to any one of claims 1 to 8.

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